Citrus fruit linked with melanoma in preliminary study

(Reuters Health) - Using data from two long-term studies of women and men, researchers found a potential link between citrus consumption and malignant melanoma of the skin.

But the study did not test whether citrus fruits were the cause of the skin cancers, and more work will be needed to confirm the connection, the authors write in the Journal of Clinical Oncology.

The results, from a single "observational" study that may not reflect the whole U.S. population, should be interpreted with caution, said senior author Dr. Abrar Qureshi of the Warren Alpert Medical School of Brown University and Rhode Island Hospital.

Qureshi worked on the study in collaboration with the Channing Division of Network Medicine at Brigham and Women's Hospital in Boston.

"Cutaneous malignant melanoma is a potentially life-threatening form of skin cancer," Qureshi said. "Although there have been recently incredible advances in the treatment of melanoma, melanoma prevention through the use of sun protection and skin cancer screening is recommended."

The researchers used data on more than 63,000 women in the Nurses' Health Study and 41,000 men in the Health Professionals Follow-Up Study, both of which ran from the mid-1980s to 2010. Every two to four years, researchers collected data on participants' dietary patterns, and the men and women self-reported health events like melanoma diagnosis, which were confirmed with medical records.

The participants answered questions about how frequently they consumed grapefruit, oranges, grapefruit juice or orange juice, and the total of these four categories was considered an estimate of "overall citrus consumption," although it does not include other citruses like lemons and limes.

Over more than 20 years of follow-up, the researchers noted 1,840 cases of melanoma. Compared to people who ate citrus less than twice a week, those who ate citrus two to four times per week had a 10 percent increased risk of melanoma.

Melanoma risk increased as citrus consumption increased, rising to a 36 percent increase in risk for people who ate the fruits more than 1.5 times per day, on average. Of the citrus fruits, grapefruit seemed to have the strongest association with melanoma.

Even accounting for varying amounts of sun exposure and the geographic location of the study participants, the association between citrus fruits and skin cancer was still high, Qureshi said.

Fresh citrus fruits contain furocoumarins, a family of photoactive compounds that can make an individual more sun sensitive, and make sun exposure more damaging to skin cells, Qureshi told Reuters Health by email.

"We are NOT recommending changing fruit consumption as these fruits and vegetables are important for overall health," he said. "However, until we learn more about these furocoumarins, those consuming fresh citrus fruits on a regular basis should be extra careful with sun exposure, and depending on their outdoor activities they should wear appropriate sunscreen, hats and sun-protective clothing."

In the U.S., there are about 30 cases of cutaneous malignant melanoma for every 100,000 individuals, according to Marianne Berwick of the University of New Mexico in Albuquerque, who wrote an editorial accompanying the findings.

It is the fifth most common cancer in the U.S. and sixth worldwide, Berwick told Reuters Health by email.

The authors of the new study were careful to account for as many other explanations as possible, but still it is too soon to generalize these findings to the average person, she said.

"This study must be replicated in order for it to be used for public health messages," Berwick said.

MIAMI, FL - JUNE 15: Doctor Antonella Tost, Dermatologist University of Miami School of Medicine, examines Michael Casa Nova,12, for symptoms of skin cancer due to sun exposure on June 15, 2011 in Miami, Florida. The federal Food and Drug Administration announced that sunscreen manufacturers are to change the labels on their products to prohibit the use of certain marketing terms. The new rules are meant to help clear up confusion about the meaning of 'sun protection factor,' or SPF, and other terms like 'waterproof.' (Photo by Joe Raedle/Getty Images)

MIAMI, FL - JUNE 15: Doctor Jonette Keri, Dermatologist University of Miami School of Medicine, displays the underside of Amy Rey's arm in contrast to the top side to compare what the sun has done to the top side as she examines her for symptoms of skin cancer due to sun exposure on June 15, 2011 in Miami, Florida. The federal Food and Drug Administration announced that sunscreen manufacturers are to change the labels on their products to prohibit the use of certain marketing terms. The new rules are meant to help clear up confusion about the meaning of 'sun protection factor,' or SPF, and other terms like 'waterproof.' (Photo by Joe Raedle/Getty Images)

MIAMI, FL - JUNE 15: Amy Rey has a mark on her skin after a biopsy was performed on a lesion to check for cancer due to sun exposure on June 15, 2011 in Miami, Florida. The federal Food and Drug Administration announced that sunscreen manufacturers are to change the labels on their products to prohibit the use of certain marketing terms. The new rules are meant to help clear up confusion about the meaning of 'sun protection factor,' or SPF, and other terms like 'waterproof.' (Photo by Joe Raedle/Getty Images)

MIAMI, FL - JUNE 15: Amy Rey has freckles on her belly, as she gets a skin exam by a dermatologist at the University Of Miami School Of Medicine, she uses sun screen since she may be more susceptible to skin cancer due to her fair skin on June 15, 2011 in Miami, Florida. The federal Food and Drug Administration announced that sunscreen manufacturers are to change the labels on their products to prohibit the use of certain marketing terms. The new rules are meant to help clear up confusion about the meaning of 'sun protection factor,' or SPF, and other terms like 'waterproof.' (Photo by Joe Raedle/Getty Images)

In this photo taken on Jan. 26, 2012, in Aurora, Colo., Jodi Duke, a 35-year-old melanoma survivor living in Aurora, shows the scar left on her arm from melanoma. Duke used tanning beds as a teen and advocated for a bill regulating tanning that failed in 2007. Colorado is one of the last states to consider tanning bed limits for children. But a proposal this year to require parental notification for UV tanning beds may run into opposition from lawmakers who have vowed to shun regulation. (AP Photo/Ed Andrieski)

Katie Donnar, 18, shows her scar from where the melanoma was on the calf of her leg Thursday, Jan. 14, 2010 in Vincennes, Ind. in front of a tanning bed like the on she used at her home and at the tanning salons. Donnar was in the sixth grade when she started using tanning beds. (AP Photo/ Daniel R. Patmore)

A bandaged Sen. John McCain, R-Ariz., takes part in a Washington news conference to discuss campaign finance reform, Monday, Feb. 11, 2002. Last week, McCain had a cancerous lesion removed from the left side of his nose which was diagnosed as the earliest form of melanoma and was removed. (AP Photo/Stephen J. Boitano)

Freckle-faced Corey Halpin, 13, shows off his big scar at his Hanover Park, Ill., home on Monday, April 18, 2005, a reminder of surgery three years ago to remove a cancerous growth from his left arm. At age 10, doctors discovered melanoma on Corey's left arm, the most serious and potentially deadly form of skin cancer that until recently was almost unheard of in children. (AP Photo/Brian Kersey)

BOSTON - MAY 20: Melanoma survivor Elissa Campbell was photographed in the Back Bay in Boston, Mass. on Monday, May 20, 2013. This is the scar where the mole was removed on the back of Campbell's leg. (Photo by Yoon S. Byun/The Boston Globe via Getty Images)